So-called ASC whetlerite charcoal (hereinafter referred to also as activated charcoal), and such charcoal containing triethylenediamine (TEDA) is the adsorbent used in Canadian armed forces respirators and collective protection filters for providing protection against chemical warfare agents. ASC charcoal was developed during the 1940's in response to the established threat of chemical weapons. The charcoal is coal typically based and contains a pore structure suitable for the removal of volatile chemicals from air.
In general, the removal of chemical warfare vapour from air is achieved by two methods, namely physisorption and chemisorption. Physisorption or physical adsorption is the primary removal mechanism and is responsible for the very large capacity of charcoal for protection against agents with relatively high (&gt;100.degree. C.) boiling points such as mustard gas (bis-(2-chloroethyl sulphide) or tabun (ethyl N,N dimethylphosphoramidocyanidate). However, toxic agents with much lower boiling points (60.degree. C.) such as hydrogen cyanide, phosgene and cyanogen chloride are not easily removed by physical adsorption. Accordingly, chemical reactive metals such as copper and chromium were added to the charcoal to provide a second removal mechanism which is commonly referred to as "chemisorption". Without the chemisorptive property imparted to charcoal by copper and chromium, the charcoal would provide little protection against hydrogen cyanide. Silver has also been used to provide chemisorptive protection against arsine. Another class of metals that may be added to the charcoal includes all oxidizing metals such as vanadium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, osmium, cobalt and rhodium. This class of metals is used for the oxidation of cyanogen, a decomposition product from hydrogen cyanide, and cyanogen chloride. A further class of metals includes silver, zinc and cadmium for the removal of low molecular weight, low boiling point toxic gases such as arsine. A whetlerization formula usually consists of one or more metals from each class. In addition, the charcoal may contain organic compounds such as triethylenediamine (TEDA) and quinuclidine which prolongs the service life of the charcoal and also enhances the protection against cyanogen chloride.
In the production of such impregnated charcoal, base charcoal (BPL) is soaked with a very concentrated ammoniacal solution of copper II and chromium VI salts and a carbonate (this process is called "Whetlerization") and then oven dried. During oven drying, water is gradually removed to increase the concentration sufficiently to exceed the solubility limit. The result is the formation of very large crystals containing copper and chromium Hexavalent chromium plays a key role as an oxidant in the removal of hydrogen cyanide (AC) and cyanogen chloride (CK). Because only the outer surface of each crystal is available for reaction, a large proportion of active metal is not used, i.e. the copper and chromium are not fully utilized. The metals and consequently the adsorbent are expensive. Moreover, because of its toxicity, the chromium VI poses a disposal problem.
The object of the present invention is to provide a solution to the above-mentioned problems in the form of (a) a relatively simple process for producing an activated carbon adsorbent for use in protection against chemical warfare agents, and (b) the product produced by such process.